In order to improve fuel economy of an automotive vehicle, there have been proposed and developed various “idling-stop” control techniques in which an engine is automatically stopped at a stop of the vehicle, when a predetermined condition is satisfied, for example, when a vehicle stopping state, in which the driver has no intention of starting the vehicle, continues for a preset time duration. According to such an idling-stop control technique, in the presence of the driver's operation corresponding to the driver's intention of starting the vehicle, for instance when the brakes are released and thus the brake system is changed from operative to inoperative, the engine is automatically restarted by inhibiting “idling-stop” operation.
On the other hand, a shift (an upshift or a downshift) of a transmission is controlled by hydraulic pressure produced by an engine-driven oil pump driven by the engine. Generally, during the previously-noted “idling-stop” operation, the engine is kept inoperative and thus there is no hydraulic-pressure supply from the engine-driven oil pump to a transmission control hydraulic unit. Hence, the transmission is kept in a disabling state of power transmission.
When the engine is restarted by inhibiting “idling-stop” operation under such a power-transmission disabling state, there is a supply of hydraulic pressure produced by the engine-driven oil pump to the transmission control hydraulic unit. Thus, a transition of the transmission to an enabling state of power transmission occurs, but there is a response delay between the engine restarting point and the time when the transmission has been changed to the power-transmission enabling state by hydraulic pressure produced by the engine-driven oil pump.
Assume that such “idling-stop” operation is inhibited to put the vehicle driving system (containing the engine) into a state suited for vehicle-driving operation during a time period corresponding to the above-mentioned response delay. In such a case, engine power output, rising as a result of the “idling-stop” inhibition, would be undesirably inputted to the transmission, not yet changed to the power-transmission enabling state but remaining kept in the power-transmission disabling state, thereby deteriorating the durability of the transmission.
To avoid this, another idling-stop control technique teaches the use of an electric-motor-driven oil pump in lieu of the engine-driven oil pump during “idling-stop” operation. According to this technique, during “idling-stop” operation, by virtue of hydraulic pressure of working oil discharged from the electric-motor-driven oil pump, the transmission can be kept in a state immediately before beginning of power transmission. Therefore, immediately when the engine is restarted by inhibiting “idling-stop” operation, it is possible to rapidly rise at least one hydraulic pressure, which pressure is used for shift control or speed-change control, up to a pressure value, above which the transmission can be kept in the power-transmission enabling state, with working oil discharged from the engine-driven oil pump. Thus, there is a less risk of undesirably inputting engine power, rising as a result of the “idling-stop” inhibition (the engine restart), to the transmission, which is not yet changed to the power-transmission enabling state. Thus, it is possible to remarkably reduce the delay of a transition of the transmission to its power-transmission enabling state, thereby effectively suppressing the durability of the transmission from being deteriorated.
However, even by the use of the electric-motor-driven oil pump as well as the engine-driven oil pump, it is difficult to certainly solve the previously-discussed problem of a deterioration of the durability of the transmission. This is because a remarkably-reduced but slight delay still exists between the engine restarting point and the point of time when a transition of the transmission to the power-transmission enabling state has been completed. To avoid this, that is to say, to certainly solve the deteriorated transmission durability occurring due to an undesirable input of engine power to the transmission not yet changed to its power-transmission enabling state, the following patent document 1 proposes and teaches an improved “idling-stop” cancellation control technique, namely, the use of a hydraulic pressure sensor. According to the technique disclosed in the patent document 1, whose controlled system is an automatic transmission rather than an engine, a pressure value of hydraulic pressure used for shift control is detected by means of the hydraulic pressure sensor after the engine restart based on “idling-stop” inhibition, and then the detected hydraulic pressure is compared to a predetermined pressure value, which is predetermined so as not to cause the previously-discussed problem. When the detected hydraulic pressure exceeds the predetermined pressure value, a start-up friction element (such as a forward clutch) of the transmission is changed from a state immediately before beginning of power transmission to a power-transmission enabling state.
Patent document 1: Japanese Patent Provisional Publication No. 2006-234013 (hereinafter is referred to as “JP2006-234013”)